Define Lightwave Antennas For Measurement Systems

COMPARED TO MICROWAVE ANTENNAS, lightwave antennas have different measurement characteristics because of their use of shorter wavelengths. This aspect makes it difficult to design lightwave antennas according to each application system. A technique for measuring the far-field radiation pattern (FFP), gain, and transmissivity of each portion of an aperture has been described by Yasushi Munemasa, Tadashi Takano, and Makoto Mita from Tokyo University of Science and the Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (ISAS/JAXA) and Masatoshi Sano from the Tokyo University of Science.

The researchers propose test systems for nearfield (NF) and far-field (FF) measurements. In the NF region, the phase distribution is measured using a Mach-Zehnder or other interferometer. The Fourier transform method is better suited to the FF measurement, as it satisfies the Fraunhofer diffraction criterion with a transformation lens. Equations are derived for calculating the radiation pattern and antenna gain from the measured values. See "Measurement of Lightwave Antennas: Difficulties and Peculiarities in Comparison with Radio-Wave Antennas," IEEE Transactions on Antennas and Propagation, November 2007, p. 3040.